Absorbent articles such as disposable diapers, adult incontinent pads, sanitary napkins and the like are generally provided with absorbent members, fibrous web structures which comprise entangled masses of fibers, to receive and retain body liquids. In order for such absorbent articles to function efficiently, the absorbent members must quickly acquire body liquids into the structure from the point of application and subsequently distribute the body liquids within and throughout the absorbent member to provide maximum liquid containment. In addition, the absorbent members should be capable of retaining liquids when placed under loads. Prior art attempts to improve the effectiveness of such absorbent members have included distributing particles of absorbent gelling material throughout or in portions of the absorbent member. For example, U.S. Pat. No. 4,610,678, entitled "High-Density Absorbent Structures" which issued to Paul T. Weisman and Stephen A. Goldman on Sept. 9, 1986, discloses absorbent members wherein particles of absorbent gelling material (hydrogel) are dispersed in an air-laid web of hydrophilic fibrous material and compressed to a particular density. In addition, U.S. Pat. No. 4,673,402, entitled "Absorbent Articles With Dual-Layered Cores" which issued to Paul T. Weisman, Dawn I. Houghton and Dale A. Gellert on Jun. 16, 1987, discloses a dual-layer absorbent core wherein an absorbent acquisition layer overlays a lower fluid storage layer that consists essentially of a uniform combination of hydrophilic fibrous material and discrete particles of absorbent gelling material.
Absorbent gelling materials are polymeric materials which are capable of absorbing large quantities of liquids such as water and body wastes relative to their weight, and which are further capable of retaining such absorbed liquids under moderate pressures. These absorption characteristics of absorbent gelling materials make them especially useful for incorporation into absorbent articles such as disposable diapers, adult incontinent pads, sanitary napkins and the like. However, in spite of the extremely high absorption capacities of such absorbent gelling materials, their performance when used in disposable absorbent articles has still not been optimized.
The effectiveness of absorbent gelling materials in disposable absorbent articles is quite dependent upon the form, position, size, and/or manner in which the particles of absorbent gelling material are incorporated into the absorbent member. In some cases, for example, the effectiveness of absorbent members containing particles of absorbent gelling material can be adversely affected by a phenomenon called gel blocking. The term "gel blocking" describes a situation that occurs when a particle of absorbent gelling material is wetted, the surface of the particles swelling so as to inhibit liquid transmission into the interior of the absorbent member. Wetting of the interior of the absorbent member, therefore, takes place via a very slow diffusion process. In practical terms, this means that acquisition of liquids by the absorbent member is much slower than the discharge of the liquid to be absorbed, and leakage from the absorbent article may take place well before the particles of absorbent gelling material in the absorbent member are fully saturated or before the liquid can diffuse or wick past the "blocking" particles into the rest of the absorbent member. The slow acquisition rate also fails to take advantage of the rapid wicking of liquids to other parts of the absorbent member provided by a densified absorbent member containing particles of absorbent gelling material.
Thus, it would be advantageous to provide an absorbent member that more quickly acquires and distributes liquids within itself while minimizing gel blocking during the liquid acquisition phase. It is therefore a primary objective of the present invention to provide improved absorbent members which are especially effective and efficient in their use of absorbent gelling materials.
It is a further object of the present invention to provide absorbent members of improved capacity and efficiency by control of the particle size distribution of the absorbent gelling materials employed in the absorbent members.